1. Field of the Invention
The present invention generally relates to semiconductor devices, and, more particularly, to a semiconductor device having a semiconductor chip on TAB (Tape Automated Bonding) tape.
In recent years, there has been an increasing demand for smaller semiconductor devices, as electronic devices have been becoming more and more efficient. In response to the trend, BGA (Ball Grid Array) type semiconductor devices are being widely used. Among the BGA type semiconductor devices, T-BGA type semiconductor devices each having a semiconductor chip attached onto TAB tape are becoming more and more popular, because the interval between the bumps can be shortened in a T-BGA type semiconductor device.
As higher reliability is also expected, semiconductor devices which can perform in a stable manner regardless of changes in ambient temperature are required.
2. Description of the Related Art
FIGS. 1 to 3 illustrate a conventional semiconductor device 1 which employs a TAB technique. More specifically, FIG. 1 is an enlarged plan view of a corner of a device hole 7 of the semiconductor device 1, FIG. 2 is a enlarged sectional view of a corner of the device hole 7 of the semiconductor device 1, and FIG. 3 is a plan view of the semiconductor device 1 prior to the severance of a TAB tape 3. For ease of explanation, an encapsulation resin 4 is not shown in FIGS. 1 and 3.
The semiconductor device 1 comprises a semiconductor chip 2, the TAB tape 3, and the encapsulation resin 4. Circuits are formed on the upper surface of the semiconductor chip 2, and a plurality of electrodes 5 surround the circuits.
The TAB tape 3 comprises a base film 6, a wiring pattern 8, a solder resist 11, and resin stoppers 12.
The base film 6 is a resin substrate made of polyimide, for instance, and is provided with a square opening that is the device hole 7. The wiring pattern 8 having a predetermined pattern is formed on the base film 6. The inner end portions of the wiring pattern 8 extend into the device hole 7 and constitute inner leads 9. The outer end portions of the wiring pattern 8 constitute terminal connection portions provided with solder balls 14 (shown in FIG. 3) as external connecting terminals.
The semiconductor chip 2 is bonded to the inner leads 9 extending into the device hole 7 by bumps 10, so that the semiconductor chip 2 is electrically connected to the inner leads 9 via the bumps 10, and is fixed within the device hole 7.
The resin stoppers 12 are formed on the base film 6, and are located at the four corners of the device hole 7. The resin stoppers 12 are formed at the same time as the formation of the wiring pattern 8, and are made of the same material as the wiring pattern 8. With the resin stoppers 12 formed at the four corners of the device hole 7, the encapsulation resin 4 can be prevented from excessively flowing out through the device hole 7 toward the back side.
The distance L1 between the semiconductor chip 2 and the base film 6 at each corner of the device hole 7 is longer than the distance L2 between the semiconductor chip 2 and the base film 6 at a location other than each corner of the device hole 7. If the encapsulation resin 4 is formed without the resin stoppers 12, the amount of resin flowing out through the gap between the semiconductor chip 2 and the base film 6 at the corners of the device hole 7 is much larger than the amount of resin flowing out through the gap at the other locations. As a result, excess resin 4A is formed as shown in FIG. 2.
To avoid such a situation, the resin stoppers 12 are formed at each corner of the device hole 7, so that the gap between the semiconductor chip 2 and the base film 6 at the corners of the device hole 7 is made almost as narrow as the gap at the other locations. Thus, the encapsulation resin 4 can be prevented from excessively flowing out through the device hole 7 toward the back side.
The solder resist 11 is further placed on the base film 6. Conventionally, the solder resist 11 is formed to surround the device hole 7. To obtain the solder resist 11, an ink-type resist is formed by a printing technique. In recent years, however, as higher-density semiconductor devices have been expected, photoresist materials on which minute processing can be performed have been used as the solder resist 11. The solder resist 11 made of a photoresist material will be hereinafter referred to as a photo-solder resist. This photo-solder resist 11 is made of an insulating resin (such as epoxy resin) which is harder than the base film 6. The photo-solder resist 11 covers the upper surface of the wiring pattern 8 so as to protect the wiring pattern 8. The photo-solder resist 11 also covers a part of the resin stoppers 12.
The photo-solder resist 11 is not formed at the inner leads 9 and at the terminal connecting portions provided with the solder balls 14. Accordingly, the inner leads 9 and the terminal connecting portions are exposed through the photo-solder resist 11.
As mentioned before, the photo-solder resist 11 is made of a resin different from the base film 6 so as to provide the protection for the wiring pattern 8 and to maintain insulation properties. Therefore, the thermal expansion coefficient of the photo-solder resist 11 differs from the thermal expansion coefficient of the base film 6.
The encapsulation resin 4 is formed to cover the device hole 7, as shown in FIG. 2, so that it can protect the semiconductor chip 2 and the inner leads 9.
The semiconductor device 1 is heated, when the encapsulation resin 4 is formed after the semiconductor chip 2 is bonded to the TAB tape 3, and when the semiconductor device 1 is mounted on a printed circuit board. As a result, thermal expansion due to rapid temperature rise is induced, and stress is caused in the TAB tape 3 due to the difference in thermal expansion coefficient between the photo-solder resist 11 and the base film 6.
Since the photo-solder resist 11 is subjected to a photo-hardening process, it is harder than the conventional resist formed by a printing technique. Furthermore, the photo-solder resist 11 is also harder than the base film 6. Because of this, stress is caused mainly in the photo-solder resist 11. Also, stress tends to concentrate at locations where there is large variation in sectional area. Accordingly, in the photo-solder resist 11 having a rectangular frame-like shape, stress concentrates at locations facing the corners of the device hole 7.
For the above reasons, the conventional semiconductor device 1 has a problem that cracks occur at the locations on the photo-solder resist 11 facing the corners of the device hole 7 at the time of heat application. If the cracks grow larger, the wiring pattern 8 might be cut off by them, resulting in poor reliability of the semiconductor device 1.